Porous fibrous web to a substrate and articles therefrom

ABSTRACT

A method of bonding a fluid-porous, fibrous, woven or non-woven web to a substrate and products made thereby. The porous web is overall or pattern coated with an extremely low level of hot-melt adhesive by causing the hot-melt adhesive to be wiped from a controlled thickness hot-melt adhesive source by the individual projecting surface fibers and fiber junctions of the porous web. Hot-melt adhesive globules are formed on the individual projecting surface fibers and fiber junctions which, when the porous web and substrate are passed through a preset clearance nip roll assembly, provide a product wherein the porous web is bonded to the substrate with excellent bond strength, the porous web remaining flexible and completely transparent to fluid transmission.

DESCRIPTION OF THE PRIOR ART

The process of the present invention may be applied in any instancewhere it is desired to provide a laminated product, at least onelamination of which comprises a fluid-porous, fibrous sheet. Anexcellent example of such a product is an integral disposable diaper.While not intended to be so limited, for purposes of exemplary showingthe present invention will be described in its application to themanufacture of integral disposable diapers.

Prior art workers have devised a number of different types of integraldisposable diapers. Generally, however, such diapers comprise threebasic parts: a moisture previous topsheet intended to lie adjacent thebody of the wearer, a moisture proof backsheet and an absorbent coretherebetween. Examples of such disposable diapers are taught in U.S.Pat. Nos. Re 26,151 and 3,860,003. The absorbent core may or may not beprovided with a layer of high wet strength tissue on one or both of itsfaces.

In a typical practice, a topsheet may be provide with an extruded beador strip of hot-melt adhesive along each of its edges. These edges arefolded about the edges of the absorbent core and are adhered to theunderside of the absorbent core. In somewhat similar fashion, extrudedhot-melt adhesive strips or beads are located on the backsheet insetfrom and parallel to its longitudinal edges. The folded edges of thetopsheet are adhered to the backsheet by means of these last mentionedadhesive strips. Additional adhesive strips or beads may be provided onthe topsheet to join it to the backsheet at the waste band areas of thediaper.

In another approach, the backsheet is provided with a plurality oflongitudinally extending hot-melt adhesive strips or beads in parallelspaced relationship. The absorbent core is applied to the backsheet andadhered thereto by the adhesive strips. The topsheet is next applied,being adhered to those edge portions of the backsheet which extendbeyond the core.

The above approaches utilizing hot-melt adhesive strips or beads resultin certain deficiencies. First of all, the adhesive usage is relativelyhigh with respect to the area actually bonded and the adhesive strips orbeads are apparent and unsightly. At the positions of the adhesivestripes or beads, the softness of the product is reduced. As a result,must work has been directed to making the strips or beads of hot-meltadhesive as thin as possible so as to be as flexible as possible.Wherever the adhesive stripes or beads are applied to, or are in contactwith, the porous, fibrous topsheet, the porosity of the topsheet is lostor seriously effected. Furthermore, in products requiring large areas ofbonding a multiplicity of adhesive strips are required in closeproximity thereby greatly exaggerating the above enumerateddeficiencies. Finally, in those prior art approaches wherein onlyperipheral gluing of the diaper components is practiced, the absorbentcore may shift or bunch due to movement of the wearer.

The present invention provides a process whereby and a product wherein ahot-melt adhesive may be applied to even large areas of the porous,fibrous topsheet and the topsheet adhered to the substrate (thebacksheet and/or the absorbent core). Hot-melt adhesive applied to theporous, fibrous topsheet in the manner taught herein provides anexcellent fiber-to-adhesive bond with very good peel and creep bondcharacteristics to substrates. Nevertheless, the adhesive issubstantially invisible; the softness of the product is retained and themoisture transparency-permeability of the topsheet is reduced only by 5%or less. Where the disposable diaper has cut longitudinal edges (as indiapers of the type taught in the above mentioned U.S. Pat. No.3,860,003) the entire edge portions of the diaper can be laminatedproducing neater and more easily cut edges.

SUMMARY OF THE INVENTION

A product is made by laminating a fluid-porous, fibrous, woven ornon-woven web to a substrate web. To this end, the porous web is patterncoated or coated overall with an extremely low level of hot-meltadhesive by causing the hot-melt adhesive to be wiped from the slotextrusion orifice of a glue nozzle (or other controllable-thicknessadhesive source) by the individual projecting surface fibers and fiberjunctions (i.e. junctions formed by overlapping or intersecting surfacefibers) of the porous web.

The liquid, hot-melt adhesive tends to form globules on the projectingsurface fibers and fiber junctions, which globules are characterized byexcellent adhesive-to-fiber attachment. It will be understood that theglobules need not necessarily be spherical and most frequently areelongated in the direction of the fibers to which they adhere and oftenin the direction of travel of the web. It has further been noted that atsites of surface fiber junctions the globules will be enlarged at thepoints of junction or cross-over of the surface fibers by virtue ofsurface tension or capillary effects. The porous, fibrous web isthereafter passed, together with the substrate web, through a presetclearance nip roll assembly whereupon the fibrous porous web becomesfirmly bonded to the substrate web. In this way, a highly porous,fibrous web can be continuously adhesively coated and laminated to thesubstrate web. Very good bond strength is achieved and at the same timethe moisture transparency/permeability of the porous, fibrous sheet isvery little affected. The adhesive is essentially invisible and theflexibility and compliance of the final product is essentiallyunaffected.

To prevent the laminating hot-melt adhesive from pressing through thehighly porous, fibrous web when being laminated to a substrate web, thelaminating nip roll contacting the porous web may be double-wrapped bythe porous web. This entails passing the porous web uncoated through thenip and then looping it back around and through the nip again, havingbeen adhesive coated in the mean time. Any adhesive "press-through"occuring during the lamination operation will be transferred onto thatportion of the uncoated fibrous web passing through the nip.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an exemplary disposable diaper in an unfoldedconfiguration and partially fragmented.

FIG. 2 is a fragmentary, diagramatic view, partially in cross section,and illustrating the application of a hot-melt adhesive to a porous,fibrous web and the laminating of that web to a substrate.

FIG. 3 is a fragmentary, semi-diagramatic, magnified bottom view (partlyin cross section) of a narrow portion of the porous, fibrous web andsubstrate of FIG. 2. FIG. 4 is a semi-diagrammatic side elevational viewof a system for applying hot-melt adhesive to a porous, fibrous web andlaminating the web to a substrate.

FIG. 5 is an enlarged, fragmentary, cross sectional view of the presetnip of FIG. 4.

FIG. 6 is a perspective view of a modified form of that nip roll of FIG.4 contacting the substrate.

FIG. 7 is a fragmentary plan view of a porous fibrous web for use as atopsheet in the diaper of FIG. 1 and pattern coated with a hot-meltadhesive.

FIG. 8 is a semi-diagramatic elevational view of a system for applyinghot-melt adhesive to a porous, fibrous web and laminating that web to asubstrate in the form of a second porous, fibrous web.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As indicated above, the manufacture of disposable diapers constitutes anexcellent application of the present invention and, while not intendedto be so limited, the invention will be described in terms thereof. Tothis end, an exemplary diaper of the type taught in the above mentionedU.S. Pat. No. 3,860,003 is shown in FIG. 1. The diaper, generallyindicated at 1, is made up of three basic parts: a flexible, moistureimpermeable backsheet 2, an absorbent core 3 and a porous, fibroustopsheet 4.

The moisture impermeable backsheet 2 may be made of any suitablematerial such as a low density, opaque polyethylene web having athickness of about 0.0015 inch. The absorbent core 3 may be any of theabsorbent materials known to those skilled in the art as for example amultiplicity of plies of crepe cellulose wadding, fluffed cellulosefibers, textile fibers, fluffed wood pulp (generally known as airfelt)or other absorbent materials. As a part of the core, a wet strengthtissue layer may be applied to that face of the core adjacent backsheet2, to that face of core 3 adjacent topsheet 4 or both. One such tissuelayer is shown at 5.

Topsheet 4 may again be made of any suitable complaint, soft feeling,porous material. In general, a topsheet for a disposable diaper is madeup of woven or non-woven fibers such as, for example, mixtures ofpolyester and rayon fibers.

In the embodiment illustrated, the absorbent core 3 is of an hour glassshape forming a back portion 3a, a front portion 3b and a crotch portion3c. Between the back and front portions of absorbent core 3 and adjacentthe crotch portion 3c the bottomsheet 2 and topsheet 4 are joinedtogether to form side flaps 6 and 7. Elastic members 8 and 9 areoperatively associated with side flaps 6 and 7, respectively, causingside flaps 6 and 7 to be gathered and to form a moisture proof seal withthe wearers legs during use. The diaper of FIG. 1 may also be providedwith attachment tapes 10 and 11, as is well known in the art.

In the assembly of such a diaper structure, it is common to present thebacksheet 2 and topsheet 4 as continuous webs. Core elements 3 andelastic members 8 and 9 are appropriately located between the topsheetand backsheet webs and the webs are caused to be joined together.Heretofor, the joiner of these elements was accomplished by doublecoated pressure sensitive tape, beads or strips of hot-melt adhesiveappropriately located on the topsheet web or the backsheet web or both,or by other attachment means or combinations of attachment means. Thesevarious attachment methods resulted in numerous deficiencies, asenumerated above.

In accordance with the present invention, attachment of the diaper partsis accomplished by applying hot-melt adhesive to the topsheet web andcausing the topsheet web to become laminated to the absorbent core andthose exposed portions of the backsheet web. The absorbent core may beadditionally attached to the backsheet web by any appropriate means, ifdesired.

FIGS. 2 and 3 diagramatically represent the gluing and laminating of aporous, fibrous web to a substrate web. For purposes of an exemplaryshowing, a porous, fibrous non-woven web 12 is shown which may beequivalent to topsheet 4 of FIG. 1. Similarly, a non-porous substrateweb 13 is illustrated which again may be equivalent to backsheet 2 ofFIG. 1. For purposes of clarity, core elements such as core element 3 ofFIG. 1 and elastic elements such as elastic elements 8 and 9 of FIG. 1are not shown in FIGS. 2 and 3.

A hot-melt adhesive is applied to the porous, fibrous web 12 by directcontact extrusion. To this end, a glue nozzle 14 is provided having aslot extrusion orifice 15. Hot-melt adhesive 16 is pumped throughorifice 15 forming a small pool of adhesive 17. As the porous, fibrousweb 12 is drawn over nozzle 14 and the adhesive pool 17, surface fibersand fiber junctions will "pick off" adhesive from pool 17. In this way,adhesive globules 16a are formed on the surface fibers and fiberjunctions having excellent adhesive-to-fiber attachment points. As shownin FIGS. 2 and 3, adhesive globules 16a are randomly located at theposition of the fibers and fiber junctions at the surface of porous web12. The porous, fibrous web 12 is thereafter immediately combined withthe substrate web 13 and webs 12 and 13 are subjected to moderatecompression forces at the point of combination, generally indicated at18. This is accomplished by a preset clearance nip roll assembly, aswill be described hereinafter. The hot-melt adhesive globules aredeformed (i.e. slightly flattened and widened under compression as at16b in FIGS. 2 and 3) to increase the total adhesive contact area to thesubstrate surface. This assures good adhesion to the substrate web 13.In instances where a cooled "skin" forms on the adhesive globules theterm "deformed" is intended to include the rupturing of the globule"skin" under compression to expose the heated interior to the substrate.

The glue nozzle 14 is a conventional slot extrusion oriffice nozzle wellknown in the art. Excellent results have been achieved, for example,through the use of such nozzles manufactured by Acumelt Labratories,Inc. of Newton Lower Falls, Mass.

Hot-melt adhesives having a wide variety of temperature characteristicsand adhesive properties are readily available. It is well within theskill of the ordinary worker in the art to select a hot-melt adhesivehaving appropriate temperature, flow and adhesive characteristics forcoating on the porous, fibrous web 12 and an application temperature toenable the adhesive globules to possess sufficient "open-time" (i.e.,time to solidification) between the application of the adhesive to theporous, fibrous web 12 and the combining of web 12 with substrate web13. For example, in applying a porous, carded non-woven fibrous topsheetweb (of 70% to 100% polyester fibers of 11/2 to 3 denier, 0% to 30%rayon fibers of 3 denier, and bonded together with 20% to 25%cross-linking vinyl acrylic latex, to achieve a total web basis weightof from 20 to 30 gm/yd² and having a thickness of from 0.008 to 0.020inch) to a polyethylene backsheet web, excellent results have beenachieved using a hot-melt adhesive manufactured by Findley Adhesives ofMilwaukee, Wis., under the formulation number 690-334 at an applicationtemperature of from about 280° F. to about 320° F. (with an open time ofup to about 1 second).

It has been determined that for best results and for any desired webspeed the hot-melt adhesive 16 should be pumped through the slotextrusion orifice 15 of nozzle 14 at a rate such that, if it were beingapplied to a smooth, non-fibrous web, a continuous, uniform adhesivelayer of from about 0.0002 inch to about 0.0010 inch in thickness wouldbe produced. This will result in globules on the surface fibers andfiber junctions of the porous, fibrous web of from about 0.001 inch toabout 0.008 inch in thickness.

A system for adhesive coating the porous, fibrous web 12 and laminatingit to the substrate web 13 is diagramatically illustrated in FIG. 4. Theweb 12, from a source thereof generally indicated at 19 is caused topass over a nip roll 20. The web 12 thereafter passes over additionalidler rolls 21, 22 and 23. After its passage about roll 23 the web 12 iscoated with hot-melt adhesive by causing it to pass over glue nozzle 24equivalent to glue nozzle 14 of FIG. 2. The coated web 12 again passesabout nip roll 20 at which time it is combined with substrate web 13passing about nip roll 25 to produce the desired laminated web assembly.FIG. 5 is an enlarged view of the nip between rolls 20 and 25 it will beevident from this figure that that portion of web 12 provided withadhesive globules 16a (and indicated at 12a) passes through the nipbetween the substrate web 13 and the initial, unglued portion of web 12,indicated at 12b. This "double-wrapping" of web 12 about nip roll 20will assure that during lamination any hot-melt adhesive pressed throughthe highly porous web portion 12a will be transferred onto the backupweb portion 12b and will not accumulate on the laminating nip roll 20.

In the preferred practice of the system of FIGS. 4 and 5, idler roll 21is so positioned that the unglued portion of web 12 will remain incontact with the glued portion of web 12 until the unglued web portionreaches idler roll 21. This will give any adhesive pressed through webportion 12a during its passage through the nip and contacting webportion 12b (see FIG. 5) an opportunity to solidify. While the amount ofadhesive "press through" or "strike-through" will be very little, anypoints of joiner between the glued and unglued porous web portions willbe cleanly broken at idler roll 21 without glue stringing or the like.

Combiner rolls 20 and 25 are set at a fixed, predetermined nipclearance. The preset nip gap should be such as to produce a softcompression force between the hot-melt adhesive treated porous, web 12and the substrate web 13. As used herein, the phrase "a soft compressionforce" is intended to mean a force sufficient to deform the globulesinto intimate contact with the substrate web and rupture the surfacefilm or the hot-melt adhesive globules 16a (if required) whileminimizing "strike-through" or "press-through" of the adhesive. As anexample, excellent results were achieved with a preset nip gap of 0.012inch during the lamination of a porous, fibrous, carded non-woven web ofthe type described above and having a thickness of 0.016 inch (doublewrapped about nip roll 20 for an effective uncompressed thickness of0.032 inch) and a polyethylene substrate web of 0.0015 inch thickness,utilizing the adhesive formulation set forth above.

When the system of FIGS. 4 and 5 is used in the manufacture of diapersof the type, for example, illustrated in FIG. 1, core elements 3 andelastic elements 8 and 9 will be introduced between the porous topsheetweb 12 and the moisture proof backsheet web 13 prior to the passage ofthese webs through the nip of rolls 20 and 25. In such an instance, theroll 25 will, as shown in FIG. 6, have a peripheral cavity 26 configuredto accept an absorbent core 3 as it passes between rolls 20 and 25. Thecavity 26 may be filled with a resilient material 27 such as foam openpore urethane elastomer or the like. The cavity 26 is so sized and theresilient material 27 is so chosen that that portion of the web assemblycontaining an absorbent core is subjected to no greater compressionforce than that portion of the web assembly which does not have anabsorbent core therebetween.

Once the core-containing web assembly has passed between the preset niprolls 20 and 25 and beyond idler roll 21, the assembly may be cut intoindividual integral disposable diapers of the type shown in FIG. 1. Thedisposable diaper products, made in accordance with the above describedprocess, are characterized by the fact that the topsheet 4 has beenfirmly bonded to the wet strength tissue element 5, those portions ofthe absorbent core 3 while extend beyond tissue 5 and those portions ofbacksheet 2 which extend beyond the core 3. The bonding of the topsheet4 to the core 3 and its wet strength tissue element 5 markedly improvesthe tearing and balling strength of the core and tends to retain thecore in its proper position during movement of the wearer. The topsheet4 having been coated with a hot-melt adhesive, nevertheless remainscompletely transparent to moisture transmission. The disposable diaperstructure is highly flexible, shows little evidence of any adhesiveattachment means and has excellent bond strengths (both peel and creep).The fact that topsheet 4 is firmly bonded to backsheet 2 particularly inthe areas of side flaps 6 and 7 makes the cutting of lateral notches 28and 29 therein both neater and easier. Despite their lamination,however, the side flaps 6 and 7 remain highly flexible and compliant.

In the manufacture of integral disposable diapers of the type shown inFIG. 1, it has been found to be unnecessary to coat the topsheet 4overall. The process described with respect to FIGS. 2 through 5 lendsitself well to the use of direct web contacting, multi-slotted, hot-meltglue applicator nozzles (well known in the art) capable of applying thehot-melt adhesive in a pattern. A porous, fibrous topsheet web fragmenthaving a pattern coating of hot-melt adhesive is illustrated at 30 inFIG. 7. The adhesive pick-up by the surface fibers and fiber junctionsof web 30 is the same as described with respect to FIGS. 2 and 3. Theweb 30 is provided with relatively wide glue area 31 and 32 along itslongitudinal edges. The wide glue areas 31 and 32 are so sized as toincorporate a portion at least of the side flaps 6 and 7 (see FIG. 1).Between the wide glue areas 31 and 32 there are a plurality of narrowglue areas 33 extending longitudinally of web 30 and in parallel spacedrelationship. The width of glue areas 33 and the spaces therebetweenhave been exaggerated in FIG. 7 for purposes of clarity. Excellentresults have been achieved, for example, with glue areas 33 having awidth of about 1/8 inch separated by non-glue areas having a width ofabout 1/4 inch.

A topsheet web of the type shown at 30 in FIG. 7 may be laminated to abacksheet web in the same manner described with respect to FIGS. 4 and5. An excellent bond with all of the advantages described above isachieved with an even greater savings in the amount of hot-melt adhesiveused.

The process illustrated in FIGS. 4 and 5 is applicable to the adheringof a porous, fibrous web to any suitable substrate web. FIG. 8illustrates a system, similar to FIG. 4, wherein a porous, fibrous webis adhered to a substrate in the form of another porous, fibrous web. Tothis end, a first porous, fibrous web 34 from a source generallyindicated at 35 is caused in unglued condition to pass about a nip roll36 and a series of idler rolls 37 through 39. The rolls 36 through 39are equivalent to rolls 20 through 23 of FIG. 4. After its passage aboutidler roll 39, the web 34 has a hot-melt adhesive applied thereto by aglue nozzle 40 equivalent to glue nozzle 24 of FIG. 4. Thereafter, theweb again passes about nip roll 36.

A porous substrate web 41 from a source generally indicated at 42 iscaused to pass about a second nip roll 43. Thereafter, web 41 passesover idler rolls 44 through 46 and again about nip roll 43 whereupon itis laminated with adhesive-coated web 34. The double wrapping of niprolls 36 and 43 will prevent accumulation of hot-melt adhesive thereonin the same manner described with respect to FIG. 4. Again, it ispreferred that idler rolls 37 and 44 be so located that the initialflights of webs 34 and 41 are stripped from the bonded web assembly31-41 by these idler rolls, should any hot-melt adhesive strike throughto the initial web flights. While for many purposes adequate bondstrength between webs 34 and 41 can be achieved through the applicationof hot-melt adhesive to web 34 only, additional bond strength can berealized by applying hot-melt adhesive to web 41 by means of a secondglue nozzle 47 shown in broken lines.

Modifications may be made in the invention without departing from thespirit of it. As indicated above, various types of substrate webs may beused in the process of the present invention. The same is true withrespect to the porous, fibrous web which may take the form, for example,of a wet-strength paper, a woven cloth or the like.

The process of the present invention may be used to apply an overallcoating on the porous, fibrous web or a pattern coating, as describedabove. Various adhesive coating patterns are possible including stripesrunning in the machine direction, wide bands, or interrupted orintermittent patterns. It is also within the scope of the presentinvention to substitite gravure wipe-coating techniques for the slotextrusion orifice nozzles taught above to provide the adhesive globuleson the surface fibers and fiber junctions of the porous web.

In an instance where it might not be convenient to combine the porous,fibrous web and the substrate web immediately after application of thehot-melt adhesive to the porous web, the adhesive globules can beallowed to solidify and can subsequently be reheated prior to thelamination step. In an instance where adhesive "press-through" or"strike-through" proves to be a particular problem, combiner roll 20 ofFIG. 4 or combiner rolls 36 and 43 of FIG. 8 could be web-wrapped morethan twice. This would entail a proper adjustment of the presentcombiner nip clearance.

In the manufacture of integral disposable diapers, it will be understoodby one skilled in the art that the topsheet need not be adhered to boththe core and the backsheet. By appropriate pattern coating of thetopsheet or the like the topsheet may be adhered to the core only or tothe backsheet only.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. An integral disposablediaper comprising a fluid porous, fibrous topsheet, a fluid impermeablebacksheet and an absorbent core element therebetween, said topsheethaving a surface overlying said core element and portions of saidbacksheet, said surface of said topsheet being defined by a plurality ofindividual fibers and fiber junctions, said topsheet being bondeddirectly to at least one of said core element and said portions of saidbacksheet by globules of hot-melt adhesive located at some at least ofsaid individual fibers and fiber junctions defining said topsheetsurface.
 2. The structure claimed in claim 1 wherein said topsheet isbonded directly to said core element and said portions of said backsheetby said globules of hot-melt adhesive located at said some at least ofsaid individual fibers and fiber junctions defining said topsheetsurface.
 3. The structure claimed in claim 1 wherein said adhesiveglobules are randomly located at the positions of said surface fibersand fiber junctions over all of said surface of said porous topsheet. 4.The structure claimed in claim 1 wherein said adhesive globules arerandomly located at the positions of said surface fibers and fiberjunctions within a pattern on said surface of said porous topsheet.
 5. Alaminate comprising a fluid-porous, fibrous layer and a substrate layer,said porous layer having a surface abutting said substrate layer, saidsurface of said porous layer being defined by a plurality of individualfibers and fiber junctions, said porous layer and said substrate layerbeing bonded directly together by globules of hot-melt adhesive locatedat some at least of said individual fibers and fiber junctions of saidsurface of said porous layer.
 6. The structure claimed in claim 5wherein said adhesive globules are randomly located at the position ofsaid surface fibers and fiber junctions over all of said surface of saidporous layer.
 7. The structure claimed in claim 5 wherein said adhesiveglobules are randomly located at the positions of said surface fibersand fiber junctions within a pattern on said surface of said porouslayer.